Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by klubnl.pl (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id v9HL2Rja024725 for ; Tue, 17 Oct 2017 23:02:30 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1e4YuH-0007Sx-K3 for rs_out_1@blacksheep.org; Tue, 17 Oct 2017 21:56:09 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1e4YuA-0007So-AX for rsgb_lf_group@blacksheep.org; Tue, 17 Oct 2017 21:56:02 +0100 Received: from omr-a018e.mx.aol.com ([204.29.186.64]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.89) (envelope-from ) id 1e4Yu6-0002ET-0p for rsgb_lf_group@blacksheep.org; Tue, 17 Oct 2017 21:56:00 +0100 Received: from mtaomg-aae01.mx.aol.com (mtaomg-aae01.mx.aol.com [172.27.1.99]) by omr-a018e.mx.aol.com (Outbound Mail Relay) with ESMTP id B72AA38000BA for ; Tue, 17 Oct 2017 16:55:55 -0400 (EDT) Received: from core-acb03f.mail.aol.com (core-acb03.mail.aol.com [172.27.24.3]) by mtaomg-aae01.mx.aol.com (OMAG/Core Interface) with ESMTP id 5611938000082 for ; Tue, 17 Oct 2017 16:55:55 -0400 (EDT) Received: from 188.192.44.165 by webjas-vab156.srv.aolmail.net (10.96.18.159) with HTTP (WebMailUI); Tue, 17 Oct 2017 16:55:53 -0400 Date: Tue, 17 Oct 2017 16:55:55 -0400 From: Markus Vester To: rsgb_lf_group@blacksheep.org Message-Id: <15f2c1f0c6c-c08-3ed7@webjas-vab156.srv.aolmail.net> In-Reply-To: MIME-Version: 1.0 X-MB-Message-Source: WebUI X-MB-Message-Type: User X-Mailer: JAS STD X-Originating-IP: [188.192.44.165] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1508273755; bh=fPOJ9BM0AizKA/Tb1noXhIuv/F8NDo2kq46tUCPYQnc=; h=From:To:Subject:Message-Id:Date:MIME-Version:Content-Type; b=7VkWS6wttE86W1V0PO0I/Uy0sgqk5Z4AlykRn3/gTa3FCtt2jspEjw8fPW6KMPU+r JismvYCaJ/oW0k3f3T+m/5/UDP4pbt7qNB0iu8fBnL6QLmMTL0NpFRECHLbPqaTCQr H3x3pJP5uCxtRL9FktkYgo/rItHHRi7sSn0oWXf0= x-aol-sid: 3039ac1b016359e66e5b5ce7 X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Hi Paul, yes, quite the opposite! The decode attempts for Stefan's nighttime 16-character transmission showed that the signal was very weak. An optimally weighted average of six evenings (Oct 10 to 15, 8.9 hours each) did not produce a decode. Using the known message content (the pop song) to reconstruct the carrier, a small peak with 8.4 dB SNR in 5.2 uHz became visible, corresponding to -11.2 dB Eb/N0 for 16 times 5.7 bits. [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (markusvester[at]aol.com) -0.0 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: 3efbf4053c1a70bbeb6c0a0cc657f05e Subject: Re: VLF: EbNaut on 2 frequencies Content-Type: multipart/alternative; boundary="----=_Part_20623_1783304610.1508273753196" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.1 required=5.0 tests=HTML_MESSAGE, MAILTO_TO_SPAM_ADDR autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false ------=_Part_20623_1783304610.1508273753196 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi Paul, yes, quite the opposite! The decode attempts for Stefan's nighttime 16-character transmission showed= that the signal was very weak. An optimally weighted average of six evenin= gs (Oct 10 to 15, 8.9 hours each) did not produce a decode. Using the known= message content (the pop song) to reconstruct the carrier, a small peak wi= th 8.4 dB SNR in 5.2 uHz became visible, corresponding to -11.2 dB Eb/N0 fo= r 16 times 5.7 bits. Comparing this result to +16.3 dB Eb/N0 from stacking three days of the 1-c= haracter message, we find that the SNR at night was around=20 16.3 + 11.2 + 3 - 12 =3D 18.5 dB weaker than during the day. The spectrograms show that the noise level (aft= er blanking) on the EW-antenna was approximately 10 dB higher at night, ind= icating that the signal must have been around 8.5 dB weaker. As a crude first Approximation to the model, we might look only at groundwa= ve and single-hop skywave. For 230 km range, the geometrical path differenc= e would be 63.3 km (1.37 lambda) for 90 km reflection height (night), and 4= 0.3 km (0.87 lambda) for 70 km (day). Assuming that the ionosphere is actin= g like a conducting surface, a vertically polarized field would be bounced = with zero phase shift (this may seem counterintuitive at first, as horizon= tal electric fields at normal incidence would be flipped. But the vertical = electric and horizontal magnetic components are not). Using equal amplitude= s for both waves, the phasing would then predict a 7 dB weaker signal at ni= ght. BTW I think that at our frequencies, ground wave losses are still negligibl= e up to a few 100 km range for all realistic types of ground, and a simple = 1/r calculation for monopole-over-perfect-groundplane will be quite adequat= e.=20 =20 Best 73, Markus (DF6NM) -----Urspr=C3=BCngliche Mitteilung-----=20 Von: Paul Nicholson An: rsgb_lf_group Verschickt: Di, 17. Okt 2017 21:01 Betreff: Re: VLF: EbNaut on 2 frequencies Here's the nighttime signal along the 88 degree bearing to Amberg, http://abelian.org/vlf/tmp/171017d.gif Quite the opposite to what signal reports suggest? The daytime signal on 88 deg isn't significantly different to 307 deg (not much anisotropy apparent at these short ranges). I don't put much faith in this model but it serves to illustrate the complicated way that signals can vary as a function of range. A major difficulty at short ranges is the ground wave calculation, knowing how much power couples into the ground wave, and the average ground conductivity and permittivity. The precise ups and downs depend critically on the amplitude and phase of ground and several sky waves. At best it is in the right ballpark in terms of typical average field strengths. (I take some comfort that LWPC doesn't do any better.) But at least we can see that it's plausible to blame propagation for the different performance of signals at Stefan's two frequencies. -- Paul Nicholson -- ------=_Part_20623_1783304610.1508273753196 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Hi Paul,
= yes, quite the opposite!
The decode attem= pts for Stefan's nighttime 16-character transmission showed that the signal= was very weak. An optimally weighted average of six evenings (Oct 10 to 15= , 8.9 hours each) did not produce a decode. Using the known message content= (the pop song) to reconstruct the carrier, a small peak with 8.4 dB SNR in= 5.2 uHz became visible, corresponding to -11.2 dB Eb/N0 for 16 times 5.7 b= its.

Comparing this result to +16.3 dB Eb= /N0 from stacking three days of the 1-character message, we find that the S= NR at night was around
 16.3 + 11.2 + 3 - 12 =3D 18.5 dB
weaker= than during the day. The spectrograms show that the noise level (after bla= nking) on the EW-antenna was approximately 10 dB higher at night, indicatin= g that the signal must have been around 8.5 dB weaker.

As a crude first Approximation to the model, we might look on= ly at groundwave and single-hop skywave. For 230 km range, the geometrical = path difference would be 63.3 km (1.37 lambda) for 90 km reflection height = (night), and 40.3 km (0.87 lambda) for 70 km (day). Assuming that the ionos= phere is acting like a conducting surface, a vertically polarized field wou= ld be bounced with zero  phase shift (this may seem counterintuitive a= t first, as horizontal electric fields at normal incidence would be flipped= . But the vertical electric and horizontal magnetic components are not). Us= ing equal amplitudes for both waves, the phasing would then predict a 7 dB = weaker signal at night.

BTW I think that = at our frequencies, ground wave losses are still negligible up to a few 100= km range for all realistic types of ground, and a simple 1/r calculation f= or monopole-over-perfect-groundplane will be quite adequate.
 &nbs= p;
Best 73,
Markus (DF6NM)



-----Urspr=C3=BCngliche Mitteilung-----
Von: = Paul Nicholson <vlf0403@abelian.org>
An: rsgb_lf_grou= p <rsgb_lf_group@blacksheep.org>
Verschickt: Di, 17. = Okt 2017 21:01
Betreff: Re: VLF: EbNaut on 2 frequencies

Here's the nighttime = signal along the 88 degree bearing to Amberg,

http://abelian.org/vlf/tmp/171017d.gif
Quite the opposite to what signal reports suggest?

The daytime signal on 88 deg isn't significantly dif= ferent to
307 deg (not much anisotropy apparent at these sh= ort ranges).

I don't put much faith in thi= s model but it serves to illustrate
the complicated way tha= t signals can vary as a function of
range. A major difficu= lty at short ranges is the ground wave
calculation, knowing= how much power couples into the ground wave,
and the avera= ge ground conductivity and permittivity.

T= he precise ups and downs depend critically on the amplitude
and phase of ground and several sky waves. At best it is in
the right ballpark in terms of typical average field strengths.

(I take some comfort that LWPC doesn't do any be= tter.)

But at least we can see that it's p= lausible to blame propagation for
the different performance= of signals at Stefan's two frequencies.

-= -
Paul Nicholson
--

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